Global positioning system (GPS) is widely used in a variety of applications, such as automobile navigation, geographic survey, satellite television program, satellite broadcasting, satellite communication, and military applications. The general function of the global positioning system is detection of the position, namely coordinates, of an object, which may be moving or maintains fixed, and calculation of distance, time, velocity and altitude of the object. Such data are of importance use in a variety of applications, which means the global positioning system is getting broader applications.
Development of the global positioning system has made a great progress in a number of applications. For example, U.S. Pat. No. 6,680,694 discloses a GPS based vehicle information system, comprising an in-vehicle system that communicates with a centralized server system via a wireless communication link. A user may specify a destination to the in-vehicle system, which transmits the specification of the destination to the centralized server system. The server system computes a route to the destination and transmits the computed route back to the in-vehicle system. The in-vehicle system may then guide the user to drive along the route.
Another example is illustrated in U.S. Pat. No. 6,690,323, which discloses a GPS receiver having emergency communication channel. When a normal GPS communication channel is interfered with, the communication of the GPS receiver can be maintained by switching to the emergency channel.
A further example is U.S. Pat. No. 6,633,814, which discloses a GPS system for navigating a vehicle, comprising vehicle carried receiver that receives a GPS signal to perform vehicle navigation based on pre-established maps and route information.
One further example is shown in U.S. Pat. No. 6,671,587, which discloses a vehicle dynamic measuring apparatus and a method using multiple GPS antennas. To realize vehicle dynamic measurement and determination of velocity, two GPS receiving antennas are installed in a vehicle and a controller is employed to detect change in carrier frequency.
When people watch TV programs or listen to radio programs in a moving vehicle, the electromagnetic waves that carry the programs are received by a frequency based receiver carried in the vehicle. In other words, the program can be correctly received once the receiver in tuned to the frequency of the electromagnetic waves that carry the program. Since the electromagnetic waves are generally omni-directional, an antenna can receives the waves without being set in a specific direction.
However, an electromagnetic signal that carries a satellite program is directional, which can be received by an antenna oriented in a particular direction. This makes it difficult to receive the satellite program in a moving vehicle for the direction is constantly changed. Thus, generally speaking, a conventional satellite program receiving device that is generally designed for use on fixed location cannot effectively and clearly receive the satellite program in a moving vehicle.
Past development of the GPS techniques, such as those discussed above, does not provide a solution for clearly receiving satellite program in a moving vehicle. The present invention is thus aimed to provide a solution for such a problem.